300 THE PENOKEE IRON-BEAIimG SERIES. 



series. When it is considered that in all probability this upper member 

 of the series once extended east and west as far as the lower members, the 

 proportion of this formation that is removed must be concluded to be much 

 greater than one-half. 



Throughout the area which the member covers, the exposures, with tlie 

 exception of a few localities, are not particularly numerous, and yet a suf- " 

 ficient number have been found and mapped to give a clear idea of the 

 nature of the rocks of the entire area. Nowhere are there full sections. 

 At Penokee gap the exposures are most numerous, but even here little more 

 than one quarter of its total thickness is uncovered. At Tylers fork the 

 exposures are also numerous, but here not more than one-fiftli or one-sixtli 

 of the member is shown. The conception of the member as a whole is 

 formed by uniting and correlating the results obtained from many detached 

 exposures. 



The rocks of the upper formation have been said to strike across the 

 country in perfect conformity to those of the Iron-bearing member (Pis. 

 v to xii). In the vicinity of Penokee gap and English lake the rocks of 

 the upper belt strike nearly east and Avest, and here the strikes of the irt)n- 

 bearing belt are approximately in the same direction. In the west part of 

 R. 2 W., Wisconsin, the iron-bearing formation begins to take a northern 

 trend and the strata of the upper belt conform to it. Through Ranges 1 W. 

 and 1 E., Wisconsin, the iron-bearing horizon has a strike from E. 25° N. 

 at the east side of R. 1 W. to about E. 30° N. at the east side of R. 1 E., 

 and to these strikes the slates above almost exactly correspond. In R. 2 

 E., Wisconsin, and R. 47 W., Michigan, in passing eastward there is a grad- 

 ual bowing towards a more easterly course in the rocks of the iron formation, 

 and tlie upper-belt rocks also show a coiTesponding bowing; and finally, 

 when Black river is reached, on the east side of T. 47 N., R. 46 W., Mich- 

 igan, the Iron-bearing and U])per slate members both strike nearly due 

 east and west. This exact correspondence of strike l)etween the two mem- 

 bers is accom})anied by as noticeable a correspondence in their dips, as 

 will readily l)e seen 1)}' an examination of the plates referi-ed to. The 

 foregoing facts could linrdly }h^ explained u|)(in an}- (ither hypothesis than 

 that (if a continuous coiiforiiial)]e series, whicli lias, as a whole, undergone 



